In a radio communication system using high frequencies as in millimeter wave communication, beamforming that concentrates power by narrowing a beam in the direction of a user terminal may be performed to compensate for a propagation loss. When beamforming is performed, beams are narrowed in specific directions in which user terminals are present, and therefore areas where high-power signal can be received may be spatially isolated from each other, thus providing an effect of suppressing interference between the user terminals present in a same space. In addition, frequency usage efficiency may be increased due to an improvement in a degree of spatial multiplexing.
Interference between user terminals present within a same cell may be reduced by thus performing beamforming. However, beam interference between adjacent cells (inter-cell interference) may occur. As a measure against inter-cell interference, a coordinated beamforming (CB) system is proposed which obtains information on a user terminal from a base station of an adjacent cell, and controls a beam so as to direct NULL (direction of the beam in which power is minimized) to the user terminal in the adjacent cell.
Incidentally, a technology is proposed which weakens transmission power for user terminals located in the vicinity of a base station, and for user terminals located in the vicinities of cell boundaries, controls frequency allocation such that frequency differs between the user terminals in adjacent beam areas. In addition, a satellite communication system is proposed which sets a plurality of regions (beam areas) on the ground in which regions radio terminals may communicate via a beam output by a satellite, and assigns different frequency bands to adjacent beam areas.